How To Tilt Solar Panels
by Damien Andrews
To achieve the greatest efficiency from a solar panel, it must be properly placed and pointed with respect to the sun's position in the sky. Solar panels deliver the most power when the surface of the panel catches the sun's rays coming straight into the plate. This is to say that to get the full benefit of the solar panel, it needs to be positioned so that it is 90° to the sun at any given moment (at its zenith). In Diagram 1 below, the solar panels installed on the roof are set for optimum performance in March and again in September – note the 90° angle of the solar panels.
As the perspective of Diagram 1 clearly shows, the sun will not be striking the solar panels early in the day or late in the day, when it is lowest on the horizons. All things being equal, the solar panels in Diagram 1 will get their maximum amount of sunlight at solar noon in March and September. Solar noon is when the sun reaches its highest point in the sky during the day. Solar noon rarely occurs at civil time (aka "clock time") noon.
Clearly, if you wanted to achieve maximum performance from a solar panel, you would have it track the sun from the time it rose until the time it set. As you might quickly imagine, this is not really practical for residential applications.
You can also see from the perspective of Diagram 1 that there is another angle to be concerned with. In order for the solar panels to be directly facing the sun at solar noon, they will have to be adjusted throughout the year. In Diagram 1, the bottom of the panels would have to be raised by many degrees to achieve optimum performance for June. Likewise, the tops of the solar panels would have to be raised substantially during December. Considering that each solar panel used in larger residential solar power systems is mounted in an elevated position and weighs 50 pounds and up, simply adjusting three times during the year can be problematic.
There are some excellent systems for suspending solar panels so that they may be adjusted throughout the year. Unfortunately, these systems are expensive, and also add to the cost of installing the solar panels. Using these systems, you can properly adjust a single solar panel in about 8-10 minutes. If you do not mount your solar panels on an adjustable system, you will have to decide how you want the solar panels oriented – all the time. Needless to say, this will cause tremendous fluctuations in produced energy over the course of the year.
It is usually suggested that permanently, non-adjustable solar panels be angled for the winter sun. If your solar power system produces adequate power at this orientation, then you'll have no problems during the more sun-intense summer months. While this approach does indeed make sense, it would not be applicable to those who have installed a solar power system on a beach house, which will not be used during winter.
Many people who decide to integrate solar power systems into their homes are disappointed with the results they get. This is largely due to the difference between what the capacity of a solar panel is versus what it will produce in a real-world situation. A solar panel advertised to produce 200 watts of power will indeed do so, but only under certain circumstances. And rarely are those circumstances achieved. A couple of things to remember so that you don't end up in this unhappy consumer position are: 1) If you're going to position the solar panels facing due south, and adjust them up and down at least three times a year, then figure you'll get about 70-75% of the solar panel's maximum performance. 2) If you're going to face the solar panels due south, but will not be adjusting them up and down throughout the year, then figure you'll only get 35-50% of the solar panel's optimum performance.
The best day of the year, for a solar power system, is sometime between June 20 and June 23 – it depends on the year. That's when the summer solstice occurs. The summer solstice is the day of the year when there is the most number of minutes of sunlight. There is also a winter solstice - the day of the winter when there is the most number of minutes of sunlight. It falls between December 20 and December 23. As you might have already extrapolated, the summer solstice has the shortest night of the year.
So then, if you are not going to have a tracking system for your solar panels, at what angle of tilt should you install them? There is no iron-clad rule for this, but there are numerous offerings. Here is one basic concept that has many followers. If you're installing your solar panels in a fixed position:
• And want the best results for year around use, install them at the angle of your location's latitude.
If you'd like to see oodles of different ideas, theories and diagrams on this topic, try searching on angle ofsolar panels or solar panel tilt on Google.
• And want the best results during winter, install them at the angle of your location's latitude plus 10°.